|As Kev says, it depends on which email system you are using - which you have not advised.|
For example, with yahoo, deleted emails go in the trash folder for a while.
This is periodically emptied at irregular intervals by yahoo. If the email you require is still there it can be moved back into a 'live' folder.
Would think other systems have the same facility, just as windows has the re-cycle bin.
Good Luck - Keep us posted.